1. Field of the invention
The invention pertains to acute methods of treating a brain disorder using heat transfer to improve brain function. Heat transfer may be combined with electrical stimulation of the brain or direct infusion of therapeutic agents into the brain to reduce or prevent the occurrence of, for example, an epileptic seizure. The method may also be used for brain disorders other than epilepsy, for spinal disorders, and for disorders of other body organs and tissues.
2. Description of Related Art
Epilepsy is a significant medical problem, as nearly 1% of the United States population is affected by this disease at any given time, constituting about 2.6 million people. The incidence of epilepsy is higher in children and in the elderly, such that approximately 3.5% of the population will have epilepsy at some point in life.sup.1, 3, 20, 21. Seizures are controllable in 70% of patients, but about 30% of patients have seizures refractory to treatment. Estimates indicate that the total lifetime costs in 1990 dollars for all of those with epilepsy newly diagnosed just in 1990 will be 3 billion dollars with slightly over 1 billion of this direct costs and the rest indirect costs. For those having controllable seizures, the cost per patient will be slightly over $4000. The figure rises to about $138,000 for patients with persistent, intractable, lifelong epilepsy. In 1991 dollars, the direct costs for the treatment of epilepsy in the United States were 1.8 billion dollars and the indirect costs amounted to 8.5 billion dollars.sup.1, 3. Thus, the disorder is a significant health problem and a need exists for improved treatments to control the disease and alleviate its burden on society as a whole.
Epileptic seizures occur because of an abnormal intensity and synchronized firing of brain cells. Generalized seizures can begin over essentially the entire brain at one time, while others, known as focal or partial seizures, begin in a localized area of the brain and then spread. Thus, both widespread and localized mechanisms appear to be involved in the occurrence of seizures. As an example, seizures manifest themselves as seizure discharges affecting the cerebral cortex, the outer most layer of the brain, though paradoxically, stimulation of the thalamus and other subcortical regions, located deeper within the brain, have been shown to not only initiate but also control or even prevent seizures. Evidence suggests that the thalamus and the substantial nigra are involved in the development of certain kinds of seizures.sup.15, 9, 41, 39, 13. Even more widespread mechanisms might be involved, as evidenced by the successful use of vagal nerve stimulation for treatment of some seizures. The vagus nerve is located in the neck and extends to the brain stem from which it has widespread connections within the brain, including branches to the thalamus.sup.32; 22. Studies have shown that chronic vagal nerve stimulation can reduce seizures by 50% or more in a third of treated patients.sup.14; 4. A vagal nerve simulator has recently been released as a commercial product. Information thus far indicates that it is moderately effective, but only rarely controls seizures completely.
In some patients, seizures are sufficiently localized such that removal of a particular area of the brain may result in complete seizure control.sup.11. Electrical stimulation provides a non-surgical means for impairing generation of localized seizures.sup.38, 32, 34, 27. In experimental animal models, drug application to a seizure focus can suppress or eliminate seizure activity.sup.10, 28, 16, 24, 33.
Hypothermia is known to have a protective effect on the brain both in experimental animal preparations and in humans.sup.5, 31, 8, 29, 18, 19. This protective effect on the brain is one of the reasons for employing hypothermia in medical procedures, such as cardiac surgery.sup.6. Hypothermia alters the electrical activity of the cortex in models of brain ischemia, and decreases the production of the excitatory neurotransmitters glutamate and dopamine.sup.7. Hypothermia also appears to reduce the occurrence, frequency, and amplitude of cortical potentials and suppresses seizure activity.sup.35, 12, 2, 40. Cooling is thought to prevent or abort seizures by reducing cortical excitability. Cooling brain tissue can be safely accomplished when properly undertaken. For example, irrigation of the temporal horn of the lateral ventricle with ice-cold liquid to cool the hippocampus has been successful in acutely altering memory functions in humans with no apparent adverse effects.sup.25.
Prevention of seizures using any of these methods implies that one knows when a seizure is occurring. Numerous of approaches toward detection of seizures have been explored.sup.36, 37, 17, 26, 30, 38, 23, 42, 43. One potential method utilizes neural networks as a means of detecting seizures. The advantage of this approach is that the computer detection may be modified to suit the individual patient. Implanted electrodes may use an algorithm based on neural networks to detect seizure activity. Alternatively, several rule based or template matching methods for seizure detection may be employed, as well as methods modeling seizures as chaotic attractors.
U.S. Pat. No. 5,713,923 to Ward et al. (Ward '923) discloses techniques for treating epilepsy using a combination of electrical stimulation of the brain and drug infusion to neural tissue. Stimulation may be directed to increase the output of inhibitory structures, such as the cerebellum, thalamus, or brain stem, or may inactivate epileptogenic areas. These methods tend to be based on chronic stimulation of brain inhibitory systems, with the goal of decreasing the background propensity to epileptogenesis. Historically, stimulation of inhibitory structures alone has not been particularly successful in seizure management. Ward '923 uses an implantable electrode to sense seizure onset, which permits regulatable stimulation of the brain during initial seizure activity. The combination of drug infusion with brain stimulation as disclosed in Ward '923, however, would fail to be effective in many types of seizures. Many drugs are not particularly stable at body temperature, rendering them unsuitable for long term storage in an implanted infusion device. Certain risks exist for patients receiving the combined therapy of Ward '923, including an increased risk for seizure propagation due brain stimulation as well as drug related side effects. Thus, while suitable for controlling some seizures, a substantial population of patients have seizures which cannot be treated using the methodology of Ward '923.
Therefore, a need exists to improve the therapeutic options available to persons with brain disorders, such as epilepsy.